1. Field of the Invention
The present invention relates to a display device including, for example, a plurality of organic electroluminescent elements arranged in a matrix, and a driving control method for the display device.
2. Description of the Related Art
Conventional self-luminous light emitting elements include, for example, organic electroluminescent elements, inorganic electroluminescent elements, and light emitting diodes (LEDs). Light-emitting element displays (display devices) are known which include a display panel in which such self-luminous light emitting elements are arranged in a matrix.
In particular, light-emitting element displays to which an active matrix driving scheme is applied have been prevailing significantly. Compared to a liquid crystal display device (LCD), the light-emitting element display exhibits a high response speed for image display and is independent from view angle. The light-emitting element display enables an increase in luminance, contrast, and image definition, a reduction in power consumption, and the like. Unlike the liquid crystal display device, the light-emitting element display requires no back light. Thus, the light-emitting element display is very advantageously characterized by enabling a further reduction in the thickness and weight of the display.
The active matrix driving scheme is applied to some of the light-emitting element displays. For these light-emitting element displays, various driving control mechanisms and methods for controlling the light emission of light-emitting elements have been proposed. For example, some known light-emitting element displays include light emitting elements for respective plural display pixels included in a display panel, and a driving circuit (hereinafter referred to as a pixel driving circuit) composed of a plurality of switching means for controlling the light emission of the light-emitting elements.
Various active driving schemes for light-emitting elements have been developed. The active driving scheme controls the light emission luminance of each of the light emitting elements for the respective plural display pixels according to a voltage value or a current value for a display signal to be written through a data line.
In general, the appropriate value of the luminance of the display varies depending on the brightness of a surrounding environment. For example, in a bright surrounding environment, human vision (eyes) gets accustomed to the bright environment. Thus, the luminance of the display is preferably relatively high. On the other hand, in a dark surrounding environment, the human vision gets accustomed to the dark environment. Thus, the luminance of the display is preferably relatively low. To allow image information displayed on the display to be easily seen by the human eyes, the luminance of the display needs to be controlled with respect to the gray level of the display data depending on the brightness of the surrounding environment.
In the conventional display, the luminance on the display panel for display data can be controlled by limiting the value of a display signal to be written to each display pixel. For example, the luminance on the display panel can be reduced by setting the maximum voltage (current) for the display signal to be written to the display pixel to a value smaller than the normal value. For example, using display signals only for low gray levels allows the maximum luminance of each display pixel to be reduced.
However, simply providing display using only low gray levels reduces the number of gray levels available for expression, thus degrading the display. Reducing the voltage value of the display signal for the maximum gray level of display data enables a reduction in the luminance on the display panel for the gray level of the display signal. However, since the voltage range is varied with gray level, the control of the voltage or the like for each gray level for each display pixel is complicated. The range over which the voltage is varied for each gray level is reduced, resulting in the need to improve the uniformity of the display panel and the reproducibility of the display signal. In this case, the variation relationship (y characteristic) of the luminance on the display panel with the gray level value of the display panel varies, thus varying display quality.